If you want accuracy, and can live with up to 100nsec of jitter (+/-50nsec), get yourself a good cyrstal-controlled 10HMz oscillator, and and use it to clock your square wave through two D-type bistables.
Use an exclusive-OR to compare the outputs of the two D-types, and whenever there's a difference, turn off the clock to the second D-type for 3,000 ticks of the 10MHz clock (for which you will need a 12-bit counter - in the past I would have used a pair of 74HCT40103 binary down counters).
formatting link
These days I'd find a programmable logic device with a least 14 latches (which is pretty small).
----------------- Bill Sloman, Nijmegen